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Expansion tank

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Member Posts: 26
I have review the wall for an answer and saw the Amtrol site. I need to replace a steel expansion tank but do not know the gallons in the system. The only info I have is the dimensions of the existing tank, so i can determine the gallons of the old tank but how do I select the bladder tank?

Thanks
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• Member Posts: 728
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• Member Posts: 26
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Thanks but I don't know system volume
• Member Posts: 238
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Is this for a house? If so use the residentil calculator. You'll need boiler net input and type of emitters.
• Member Posts: 26
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Commercial building,Thank
• Member Posts: 7,397
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Commercial building,Thank

You'll need to estimate the system volume. There are online calculators that will tell you how much a given size pipe holds. That, plus the volume of your boiler and emitters will give you the amount to enter in the Amtrol calculator.
Bob Boan
You can choose to do what you want, but you cannot choose the consequences.
• Member Posts: 238
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As Iron said it's a little more involved.
But too big is never a bad thing.
• Member Posts: 11,102
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For what it is worth; the IBR manual has a "rule of thumb" for air cushion tanks (what you have now) of a volume of 1 gallon for each 5,000Btuh of total heat load.

For bladder tanks they use 1 gallon of volume for each 7,000Btuh of total heat load.
You could do the math to back engineer the existing tank to see what they might had used for a factor. And then use the calculated "heat load" with the bladder formula.
Be aware that this is the residential guide, not commercial.
Assuming that existing tank is large enough but is leaking??
• Member Posts: 26
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So are you saying that even though I know that the existing tank is a 64 gallon tank, I cant convert that to something in a bladder tank ?
• Member Posts: 11,102
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Is it leaking??
• Member Posts: 26
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yes
• Member Posts: 11,102
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It would seem that Amtrol would have a simple replacement chart somewhere. They want to sell tanks. Somewhere they have a replacement guide for well/pump tank cross reference and this seems like a similar situation. (Not the same application of course, but same problem). FWIW
• Member Posts: 11,102
edited March 2015
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Again FWIW; From Dan's book "How Come", page 31: Standard steel compression tank gallons X .55 if building is 2 stories tall or by .44 if 3 stories tall. Answer is volume of diaphragm tank.
( again be aware that this is residential??) Again bigger is better.

That book also mentioned the "Vent-Rite" brand of tanks. Maybe check their site if they are still around.
• Member Posts: 22,467
edited March 2015
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Good info at the weasel site also, a better sizer program for non diaphragm type tanks

Remember the difference air control or air management

A plain steel compression type will be much larger, compared to a diaphragm or bladder style tank, as the air bubble is captive and maintained.
Www.westank.com
Bob "hot rod" Rohr
trainer for Caleffi NA
Living the hydronic dream
• Member Posts: 23,635
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JUGHNE said:

It would seem that Amtrol would have a simple replacement chart somewhere. They want to sell tanks. Somewhere they have a replacement guide for well/pump tank cross reference and this seems like a similar situation. (Not the same application of course, but same problem). FWIW

Not the same application nor the same problem as a well/pump tank arrangement at all. The ONLY similarity is that one is using an air cushion for something.

Frankly, if you don't understand that, it's unlikely that you will be able to understand how either an expansion tank (for hydronic) or a cycle control tank (for a well pump) works, and you certainly won't be able to size one correctly.

Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 11,102
edited March 2015
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Jamie, I understand very well how both type of tanks operate. My point was if they have a cross reference chart for water well tanks it seems there would be a cross reference from air cushion tanks to bladder.
If the 64 gallon volume steel tank was large enough for the system then it should be a simple cross to bladder.
And when replacing well water tanks in the past I would always go as large as space and money permitted for replacement.
For that hydronic tank above I would go with the closest estimate and leave a tee in the piping to add 2nd tank if needed.
Most likely ASME tank required so some money involved.

Also; I am interested in this post as I may have the same replacement job in the near future.
• Member Posts: 23,635
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There is a simple relationship for expansion control tanks for hydronic systems. Unfortunately, you do have to know the volume of water in the system, either the maximum operating temperature or the heat load, and also the operating pressure. Those variables don't seem to be known, at least for this thread; indeed, the OP specifically stated that he didn't know the water volume in the system.

Well pump control tanks are sized on the basis of controlling the cycle time of the pump itself, and are related to the flow rate of the pump and the cutin and cutout pressures of the pump.
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 11,102
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Could we assume that the original designer/engineer knew the total volume of piping, radiation and boiler. Temp and pressure parameters etc. And then he, the designer, probably a long time ago, chose the 64 gallon air cushion tank. And we assume that it was sufficient for the system and the PRV didn't dribble or open. Then could we say the 64 gallon is correct, maybe even a little oversize? (safe engineering)
Then the question is what size bladder tank would do the same job that the original 64 gal air cushion tank did??

As far as well tanks, there is a minimum size of course, but oversizing above minimum or using multiple tanks with matching air charges reduce pump cycling. Saving pressure switch, motor start components and rapid movement of the membrane(s) itself, prolonging tank life. That is another subject in its self.

PS; sorry Jamie I hit the LOL on your post accidently
• Member Posts: 23,635
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Absent any other information, sizing on the basis of the old 64 gallon tank would probably work just fine...

And don't worry about the LOL!
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 2,261
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JUGHNE said:

PS; sorry Jamie I hit the LOL on your post accidently

Just click it again and it will go away.
• Member Posts: 11,102
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Harvey, thanks for info, it is really good to have younger people around computers for us older folks. The LOL has left the wall.

However the question still remains on what size of bladder tank equals the old 64 gal tank?
• Member Posts: 2,261
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If the existing tank is properly sized, the answer is very simple. Start with a cold system and the exp tank drained. Reopen the fill valve and fire the boiler with all zones on. Once the boiler reaches high limit (180) close the valve to the compression tank. Drain the compression tank into 5 gallon buckets till empty. The gallons that you drained out will be the acceptance volume for the new bladder tank.
• Member Posts: 23,635
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Clever, Harvey. I'll have to remember that. Thanks!
Br. Jamie, osb
Building superintendent/caretaker, 7200 sq. ft. historic house museum with dependencies in New England
• Member Posts: 2,261
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If the existing tank is properly sized, the answer is very simple. Start with a cold system and the exp tank drained. Reopen the fill valve and fire the boiler with all zones on. Once the boiler reaches high limit (180) close the valve to the compression tank. Drain the compression tank into 5 gallon buckets till empty. The gallons that you drained out will be the acceptance volume for the new bladder tank.

Actually there is one more step.
You have to measure the initial fill water that enters the exp tank till it reaches system pressure, and subtract this amount from the amount that is extracted after the system reaches 180.

The bladder tank will be precharged. Current tank isn't.
• Member Posts: 11,102
edited March 2015
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I really like a simple solution to such a conundrum. But I always have another question. As you open the tank fill valve before any hot water is produced, the tank will fill up about a third full. And then fire up to limit and more water should enter the tank?

So the water added by thermal expansion plus the priming water for cold fill should equal the volume of a bladder tank?

I don't know, I don't deal with that many exp tanks. As I mentioned one of these for change out might be in my future.
But if your theory is correct you could have been hired by Thomas Edison. Part of his interview for engineers was to ask them to tell him the volume of a glass light bulb, not a simple shaped item. Those who measured and did a lot of complicated math were not hired. The ones who filled the bulb with water or sand (there are both versions) and dumped it into a measuring cup were deemed worthy of consideration for employment. I guess he was looking for common sense engineers.

Edit: I always said I type to slow, referring to your "one more thing", (Colombo)
PS Edit: you might still have a future with Edison.
• Member Posts: 26
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All interesting but the questions still remains.
• Member Posts: 998
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In the old days when the bladder tanks first came out, a 30 gallon expansion tank was replaced by a EX30 and a 60 by a EX60. Depending on the input of the boilers and the operating temperaturre, you can either use an EX60 or a SX60. Amtrol does have literature to help you out. amtrol.com/media/documents/extrol/MC2680_01_15_EXTROL_Brochure.pdf
• Member Posts: 4,469
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I would have probably called tech support.
• Member Posts: 26
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Just FYI if this changes anything for any of you . The input on the boiler is 1.2 mil
• Member Posts: 11,102
edited March 2015
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Is an ASME tank required for this application?

Whenever I have a question like this in any of the trades I do, (electrical, HVAC & hydronics/steam), I run the problem by one of my Wholesale houses who has someone skilled in that trade.
They have an interest in selling things, but not overselling/oversizing as they know you may ask 2 other houses for the same advice. And if they have any creditably they will sometimes eat their own mistakes.
I always double check on my own as to their sizing advice, and ask them questions if something seems way out.

They may also have a simple method to change the air handling/elimination if you go with a bladder tank.
• Member Posts: 26
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I know the difference between bladder and diaphragm tanks physically, but when would you use each one.
• Member Posts: 11,102
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I'm not familiar with which would be the best choice for your application. Hopefully someone on the wall here will help us both out.
• Member Posts: 7,356
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Bladders can be replaced, which is a pretty big deal when you look at the cost of an ASME tank. Diaphragm tanks cost less (a LOT less if you don't need an ASME stamp) but are not repairable.
• Member Posts: 26
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So no real function difference. When would you need as ASME tank
• Member Posts: 11,102
edited March 2015
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IMHO:
Your leaking old tank may or may not be stamped ASME.

But what probably matters today is:
Does your local or city codes require it for commercial application?

If the boiler is subject to annual insurance inspection, the company may insist on the ASME stamp.

As you check price the differences you see it would be good to inquire.
• Member Posts: 7,265
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Use this chart and folder. Page 5 of this PFD. It is rounded off to the BTU input of the boiler and the type of radiation.

There may be other issues. But this one makes assumptions of size. A #60 or # 90 covers most all.

http://www.amtrol.com/media/documents/extrol/MC2680_01_15_EXTROL_Brochure.pdf
• Member Posts: 7,265
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Just FYI if this changes anything for any of you . The input on the boiler is 1.2 mil

That would be found in a commercial rated tank. It would need a ASME rating. You probably need a floor mounted tank. What I posted is for a residential application.

On another note, I don't believe that any water enters a pre-charged Extrol type tank until the pre-charge level is reached.

• Member Posts: 26
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Great thanks for all your help
• Member Posts: 184
edited March 2015
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In our area...............if any SINGLE appliance is rated at greater than 199,000 btuhs or has a greater than 119 gallon capacity, ASME is required. (now you know why there are 119 gallon 199,000btuh water heaters out there
• Member Posts: 15,827
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In Mass. (and I think everywhere else) the State boiler inspectors require ASME expansion tanks if the relief valve on the boiler is above 30 psi. 30 and below non ASME tanks are ok, Above 30 ASME tanks. Hope this helps.
• Member Posts: 11,102
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Don, that ASME requirement is the same in NE, I believe.

But is the requirement for the appliance only? Not the expansion tank?

I can see a lot of money in the investment.
Again the OP needs to see what is required in his area.